SelectMany for flattening in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to flatten the list of lists using LINQ.

C Sharp (C#)

var numbers = new List<List<int>> { new List<int> {1, 2}, new List<int> {3, 4} };
var flat = numbers.[1](x => x).ToList();

Drag options to blanks, or click blank then click option'

AOrderBy

BSelect

CSelectMany

DWhere

Attempts:

3 left

💡 Hint

Common Mistakes

Using Select instead of SelectMany returns a list of lists, not a flat list.

The SelectMany method flattens a collection of collections into a single collection.

2fill in blank

medium

Complete the code to flatten and filter numbers greater than 2.

C Sharp (C#)

var numbers = new List<List<int>> { new List<int> {1, 2}, new List<int> {3, 4} };
var result = numbers.[1](x => x).Where(n => n > 2).ToList();

Drag options to blanks, or click blank then click option'

AOrderBy

BSelect

CWhere

DSelectMany

Attempts:

3 left

💡 Hint

Common Mistakes

Using Select only returns nested lists, so Where filters lists, not numbers.

SelectMany flattens the list, then Where filters numbers greater than 2.

3fill in blank

hard

Fix the error in the code to flatten the list of arrays.

C Sharp (C#)

string[][] words = { new string[] {"apple", "banana"}, new string[] {"cherry"} };
var flatWords = words.[1](w => w).ToList();

Drag options to blanks, or click blank then click option'

ASelectMany

BSelect

CWhere

DOrderBy

Attempts:

3 left

💡 Hint

Common Mistakes

Using Select causes flatWords to be a list of arrays, not strings.

SelectMany flattens the array of arrays into a single list of strings.

4fill in blank

hard

Fill both blanks to flatten and select the length of each word.

C Sharp (C#)

var words = new List<List<string>> { new List<string> {"cat", "dog"}, new List<string> {"bird"} };
var lengths = words.[1](w => w).Select(word => word.[2]).ToList();

Drag options to blanks, or click blank then click option'

ASelectMany

BSelect

CLength

DCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using Select instead of SelectMany keeps nested lists.

Using Count instead of Length on strings causes errors.

SelectMany flattens the list, then Length gets each word's length.

5fill in blank

hard

Fill all three blanks to flatten, filter words longer than 3, and convert to uppercase.

C Sharp (C#)

var words = new List<List<string>> { new List<string> {"cat", "dog"}, new List<string> {"bird", "fish"} };
var result = words.[1](w => w).Where(word => word.[2] > 3).Select(word => word.[3]()).ToList();

Drag options to blanks, or click blank then click option'

ASelect

BLength

CToUpper

DSelectMany

Attempts:

3 left

💡 Hint

Common Mistakes

Using Select instead of SelectMany keeps nested lists.

Using Count instead of Length on strings causes errors.

Forgetting parentheses on ToUpper causes errors.

SelectMany flattens the list, Length filters words longer than 3, and ToUpper() converts words to uppercase.